The present invention is related, as is indicated, to a lightning strike detection and mapping system. More particularly, the present invention relates to a system capable of sampling input signal waveforms and processing such waveforms; in a manner which provides fast, accurate information on the location of lightning strikes.
It is well known that thunderstorms present a serious threat to airborne craft as a result of the dangerous turbulence, up and down drafts, wind shear and other violent atmospheric disturbances generated thereby. Thunderstorms for the most part are comprised of clusters of cells which grow and dissipate within the storm through a variety of stages. Most of the violent lightning occurred coincidentally with the violent atmospheric disturbances during the mature stage of the storm cells. This strong correlation between the threatening atmospheric disturbances and electrical discharges was used by Ryan to create a weather mapping system known as Stormscope.RTM., which was disclosed in the U.S. Pat. No. 4,023,408 which is currently assigned to the same assignees as the instant application.
The Ryan system is capable of measuring pulse type electromagnetic radiation generated through the atmosphere from the large electric currents flowing within the lightning channel during a lightning stroke for the detection thereof. Ryan's system used an inverse relationship of the measured radiation to map the detected lightning strike on a display in range and bearing relative to an observation location which, for example, may be the location of the aircraft. In one embodiment, the observation location was calibrated at the center of the display screen and each displayed stroke appeared as a substantial point source at a bearing and radial dimension from the screen center, the radial dimension being proportional to the range measurement of the corresponding lightning stroke.
The dimension between the displayed stroke and screen center was not necessarily a measure of the actual range from the aircraft to the stroke but rather an approximation of range based on a mix of distance and intensity information of the detected lightning stroke. The Ryan system did not take into account the variety of lightning strikes, like return strikes, leader strikes and intra cloud strikes, nor did the system utilize the different frequency and pulse width characteristics of these different strikes.
While the Ryan technology described by the aforementioned '408 patent has met and continues to meet a significant commercial need, further improvements are always desirable. For example, by classifying the detected lightning strike into a known type, the range and bearing measurements corresponding thereto may be more accurately estimated to narrow the statistical distribution thereof, thus rendering a more accurate range and bearing measurement over a given region for display mapping purposes.
From the teachings of Hans Volland in his edited text "CRC Handbook of Atmospherics", Vol. I, published by CRC Press, Inc. of Boca Raton, Fla. (1982), it is recognized that impulse forms of lightning currents may be characterized into different types by the spectral frequency and pulse width characteristics thereof. A Type 1 current is observed from lightning channel currents of return strikes and commonly referred to as aperiodic waveforms. A Type 2 current is observed from both return and intra cloud strikes and is referred to as damped oscillatory waves. And, Type 3 or K current is a special case of Type 2 and is sometimes referred to as the intermediate type. A more recent model of the Ryan Stormscope technology, referred to as WX-1000, manufactured by BFGoodrich FlightSystems, Inc. and marketed more than one year prior to the filing of the instant application, used pulse width measurements of the lightning strikes to discriminate intra cloud and leader strikes from the others.
In addition, a U.S. Pat. No. 4,672,305 issued to Coleman is directed to a lightning detection system which uses a ratio of low (1.5 kHz) and high (500 kHz) frequency magnetic field components to extend the range thereof. Further, U.S. Pat. No. 4,803,421, and its divisional counterpart U.S. Pat. No. 4,873,483 both issued to Ostrander and assigned to the same assignee as the instant application, are directed to lightning detection and mapping systems which determine lightning locations from the ratio of the integrated intensity of two different field components of lightning generated signals. Also, a data acquisition system for use in gathering lightning strike data is present in the paper "A Lightning Data Acquisition System", authorized by B. M. Stevens, Jr. et al. for the International Aerospace and Ground Conference on Lightning and Static Electricity at Dayton, Ohio, Jun. 24-26, 1986.
Another U.S. Pat. No. 5,295,071 and currently assigned to the same assignee as the present application, uses a filter-based method for estimating the location of the lightning strike. The lightning strike signal is passed through a series of narrow-band filters and the filter outputs are used to determine the range and bearing of the lightning strike.
An area for improvement over the lightning detection systems in the past is additional criteria for analyzing the waveform signals rapidly and accurately to determine the location of a lightning strike. Still another area for improvement is in sensitivity and/or dynamic range of such systems. An improved dynamic range could extend the maximum range at which a valid lightning strike can be detected and mapped to an estimated location.